In vitro inhibition of demineralization from bioglass-containing adhesive and composite.

PURPOSE: To measure and compare the area of inhibition around a bioglass-containing adhesive and resin-based composite following an in vitro artificial caries model in human extracted teeth. METHODS: Preparations were made at the CEJ of extracted human molars (40, n=10/material) and restored with combinations of a bioglass-containing adhesive (BA, Regen), a reference adhesive which served as a negative control (RA), a bioglass-containing composite (BC, Regen), and a reference composite which served as a negative control (RC): BABC, RABC, BARC, RARC. All materials were light-cured and then finished with a polishing disc. Teeth were incubated (37°C) for 24 hours in water. A demineralization solution composed of 0.1 M lactic acid, 3 mM Ca3(PO4)2, 0.1% thymol, and NaOH (to adjust pH= 4.5) and a remineralization solution composed of 1.5 mM Ca, 0.9 mM P, and 20 mM Tris(hydroxymethil)-aminomethane (pH= 7.0) were prepared. Specimens were placed in the demineralization solution for 4 hours followed by a remineralization solution for 20 hours and cycled daily for 30 days. The specimens were embedded, sectioned into 100 µm sections, and the interface between the adhesive/composite and root dentin margin was viewed with polarized light. A line was drawn parallel with the zone of demineralization for each tooth. The area of "inhibition" (defined as the area external to the line) or "wall lesion" (defined as the area internal to the line) was traced with internal image evaluation software and measured. Areas of inhibition were measured as positive values and areas of wall lesions were measured as negative values. RESULTS: A one-way ANOVA found significant differences between materials for "inhibition/wall lesion" areas in root dentin (P< 0.001). Tukey post-hoc analysis ranked materials (µm2, mean± SD): BABC (3590± 2847)a RABC (1903± 1025)a, BARC (-792± 850)b, RARC (-2544± 1760)b. CLINICAL SIGNIFICANCE: The use of bioglass-containing resin-based composite with or without a bioglass-containing adhesive demonstrated inhibition of demineralization at the restoration margin.

Inhibition of root dentin demineralization by ion releasing cements.

OBJECTIVES: To compare the ability of resin-modified glass ionomer (RMGI) and bioactive cements to prevent root dentin demineralization. MATERIALS AND METHODS: Fifty molars were prepared at the cementum-enamel junction (n = 10) and restored with three bioactive cements (Activa Bioactive Cement, ACT; Ceramir Crown and Bridge, CER; and Theracem, THE), a self-adhesive resin cement (Rely X Unicem 2, UNI), and a RMGI cement (Rely X Luting Plus, LUT). Specimens were cycled for 30 days between a demineralization solution (pH = 4) composed of 0.1 M lactic acid and 3 mM Ca3 (PO4 )2 for 4 hours and a remineralization solution (pH = 7.0) composed of 1.5 mM Ca, 0.9 mM P, and 20 mM Tris(hydroxymethyl)-aminomethane for 20 hours. Specimens were sectioned to 100 µm and evaluated with polarized light microscopy. A line was drawn parallel with the zone of demineralization for each tooth. The areas of "inhibition" (external to the line) were measured as positive values and "wall lesions" (pulpal to the line) were measured as negative areas. RESULTS: Significant differences were found between materials for "inhibition/wall lesion" areas in root dentin (P < .001) and ranked as (µm2 , mean ± SD): LUT (7700 ± 2500) > CER (3800 ± 1900), THE (2100 ± 2600), and ACT (1400 ± 700) > UNI (-2000 ± 1700). CONCLUSIONS: Bioactive cements showed net areas of demineralization inhibition albeit at a lower level than a reference RMGI cement. CLINICAL SIGNIFICANCE: RMGI or bioactive cements may be indicated for patients at risk of secondary caries around crown margins.

Effect of Surface Treatment and Cement on Fracture Load of Traditional Zirconia (3Y), Translucent Zirconia (5Y), and Lithium Disilicate Crowns.

PURPOSE: To determine if surface treatment and cement selection for traditional 3 mol% yttria partially stabilized zirconia (3Y-PSZ), "translucent" 5 mol% yttria-stabilized zirconia (5Y-Z), or lithium disilicate crowns affected their fracture load. MATERIALS AND METHODS: Crowns with 0.8 mm uniform thickness (96, n = 8/group) were milled of 3Y-PSZ (Lava Plus), 5Y-Z (Lava Esthetic), or lithium disilicate (e.max CAD) and sintered/crystallized. Half the crowns were either particle-abraded with 30 µm alumina (zirconias) or etched with 5% hydrofluoric acid (lithium disilicate), and the other half received no surface treatment. Half the crowns from each group were luted with resin-modified glass ionomer (RMGI, RelyX Luting Plus) and half were luted with a resin cement (RelyX Unicem 2) to resin composite dies. Crowns were load cycled (100,000 cycles, 100 N force, 24°C water) and then loaded with a steel indenter until failure. A three-way ANOVA examined the effects of material, cement, and surface treatment on fracture load. Post-hoc comparisons were performed with the Tukey-Krammer method. RESULTS: Fracture load was signficiantly different for materials and cements (p < 0.0001) but not surface treatments (p = 0.77). All lithium disilicate crowns luted with RMGI failed in fatigue loading cycling; 3Y-PSZ and 5Y-Z crowns luted with resin showed a higher fracture load compared with RMGI (p < 0.001). With resin cement, there was no signficant difference in fracture load between 5Y-Z and lithium disiliciate (p = 1) whereas 3Y-PSZ had a higher fracture load (p < 0.0001). CONCLUSIONS: Cement type affected fracture load of crowns but surface treatment did not. The 0.8 mm uniform thick crowns tested benefited from using resin cement regardless of type of ceramic material. Crowns fabricated from 5Y-Z may be particle-abraded if luted with resin cement.

Intraoral Air Abrasion: A Review of Devices, Materials, Evidence, and Clinical Applications in Restorative Dentistry.

Intraoral air abrasion is a technique in which abrasive particles are used to remove or alter tooth structure. Intraoral air-abrasion devices are available as standalone units that offer a variety of customization, such as modifications to air pressure, particle flow rate, and water flow rate, or as attachments to a dental unit, allowing for a smaller footprint in the operatory. Some devices used for intraoral air abrasion are able to limit excess particle spray through utilization of a shroud of water. Aluminum oxide, or alumina, is the most commonly used and most abrasive type of air-abrasion medium; it is used mostly to roughen or remove tooth structure. Other types of particles are intended for cleaning tooth surfaces. Previous research has reported negative and positive effects, as well as no effect, of air abrasion on the bond to dentin and enamel. The results of a study performed for this review show that air abrasion to both dentin and enamel with alumina at 60-psi pressure produced a visible roughening texture but did not negatively affect bond strength. Clinical applications for intraoral air abrasion in restorative dentistry include cavity preparation, cleaning of preparations, and removal of plaque and stain prior to restoring a tooth.

Interference factors regarding the path of insertion of rotational-path removable partial dentures.

BACKGROUND: The aims of this study were to evaluate the effect of the location of the rotational center and the morphology of teeth resulting in interference with the rotational path of insertion and to estimate when an interference test should be performed. METHODS: A total of 400 dental radiograms of maxillary and mandibular first and second molars (100 for each position) were selected. The radiograms were used to hand-sketch the outlines on tracing paper. Then, an interference test was simulated using calipers. Mesial long occlusal rest seats with three different lengths were designed. A curve-simulated rotational path was drawn on the tracing paper showing the outline of a molar. If the curve was intersected by the mesial outline, interference was occurred. A total of 1200 tests were performed. RESULTS: A significant number of interference cases (18.5%, N = 400) occurred when the rotational center was placed at the most distal margin of the occlusal surface. The interference was reduced (2.75%, N = 400) but still present at the distal fourth of the occlusal surface. At the distal one-third of the occlusal surface, interference did not occur (0%, N = 400). There was a significant difference between the results of the three rotational centers (p < 0.0001). CONCLUSIONS: The interference test was not required for a rotational center at the distal third to half of the occlusal surface. However, if the length of the long occlusal rest extends beyond the distal third, an interference test is recommended before final impression.